In a semiconductor device manufacturing process, a plasma processing apparatus is used for processing a target object. A capacitively coupled plasma processing apparatus is known as an example of the plasma processing apparatus. The capacitively coupled plasma processing apparatus includes a chamber main body, a stage, an upper electrode, a first radio frequency power supply, and a second radio frequency power supply.
The chamber main body provides an inner space and is grounded. The stage is provided in the inner space of the chamber main body. The stage is configured to support a target object mounted thereon. The target object is mounted on the stage to be positioned on the central axis of the chamber main body. The stage includes a lower electrode. The upper electrode is provided above the stage. The first radio frequency power supply mainly supplies first radio frequency waves for plasma generation. The first radio frequency power supply is electrically connected to the lower electrode or the upper electrode. The second radio frequency power supply mainly supplies second radio frequency waves for attracting ions to the target object. A frequency of the second radio frequency waves is lower than that of the first radio frequency waves. The second radio frequency power supply is electrically connected to the lower electrode.
When the first radio frequency power supply is connected to the upper electrode, a ground conductor covers the upper electrode. The ground conductor has a cylindrical shape. A space surrounded by the ground conductor is provided above the upper electrode. The upper electrode and the first radio frequency power supply are connected through a power feed conductor. The power feed conductor extends from the upper electrode to the outside of the ground conductor while passing through the space surrounded by the ground conductor, and is connected to the first radio frequency power supply. The plasma processing apparatus is described in Japanese Patent Application Publication No. 2006-270017.
Electric field intensity distribution in which an electric field intensity is high above the center of the target object and low above the edge side of the target object is generated in the inner space of the plasma processing apparatus. In other words, the non-uniform electric field intensity distribution in which the electric field intensity is decreased as a distance from the central axis in a radial direction is increased is generated in the inner space. This tendency is remarkable when the frequency of the second radio frequency waves is high. Under such electric field intensity distribution, the plasma density is high near the central axis and low at a position far from the central axis. In other words, the plasma density is non-uniformly distributed in a radial direction with respect to the central axis.
In order to obtain uniform distribution of the plasma density under the above-described electric field intensity, it is considered to generate distribution of a magnetic field having a small horizontal component near the central axis and a large horizontal component at a position far from the central axis in the inner space of the chamber main body. Such magnetic field distribution can be generated by providing an electromagnet on the upper electrode. However, when the electromagnet is disposed in the space surrounded by the ground conductor, the first radio frequency waves flow into the electromagnet and/or a wiring connecting the electromagnet and a power supply. Accordingly, the electric field intensity in the inner space of the chamber main body varies locally. Therefore, it is required to uniform the distribution of the plasma density by the electromagnet arranged outside the ground conductor.